Abstract
Selected composited samples from Lewumeji (0-111m) and Idogun (0- 54m) Abeokuta Group, Eastern Dahomey Basin, were subjected to detailed lithologic and geochemical studies. The studies aimed at determining the lithological sequence, paleoenvironments of deposition, tectonic settings, provenance, weathering history and the classification of sediments. The core samples were subjected to lithological description and geochemical analysis were done following standard procedure through the use of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) through lithium metaborate fusion method.The lithologies from both wells consist of reddish to brown colour, rounded to sub rounded sandstone, brownish clay, and dark grey shale denoting possibly fluvial, brackish, lagoonal and marine environments. The sandstone revealed dominance of quartz which were classified as quartz arenites to sublitharenite and subarkoses, this suggests a recycled orogen source for the sandstones. Shale in the study area shows patches of CaCO 3 indicating the presence of biogenic materials. And the reddish brown colouration of clay suggests ferruginization. The geochemistry revealed low values for K 2 O/Al 2 O 3 ratio coupled with high average values of Plagioclase Index of Alteration (81.64% and 73.80%), Chemical Index of Alteration (79.22% and 71.52%) and Chemical Index of Weathering (82.41 % and 75.03%) for Idogun and Lewumeji wells respectively. This values indicate intense weathering condition. The plots of Log (Fe 2 O 3 /K 2 O) against Log (SiO 2 /Al 2 O 3 ) revealed sediments dominated by Fe - sand and Fe - shale. Also, Al 2 O 3 -(K 2 O+CaO+MgO)-(Fe 2 O 3 +MgO), (AKF) ternary plots reveals that the sediments are derived from continental environment. The Log (K 2 O/Na 2 O) against SiO 2 and the discriminant function plots indicate sediments deposited within the passive margin. Also, the Trace elements ternary plots of Th-Sc-Zr/10 and Th-Co-Zr/10 reveal deposition within Continental Island Arc and Passive Margin. The discriminant function plots characterized the sediments as Mafic Igneous rock and quartoze sedimentary provenances with minor input from Intermediate and felsic igneous provenances. The chondrite normalized REE plots show enrichment of Light REE over Heavy REE in the study area with negative Europium and Cerium anomalies greater than 1. This indicated an oxidising and a shallow marine environments. The REE pattern is similar to those for the Upper Continental Crust sediments (UCC). Conclusively, the study shows that the sediments in the study area have multiple provenances subjected to high weathering conditions and were deposited within an oxidizing and continental to shallow marine settings. Keywords: Dahomey Basin, lithostratigraphy, paleoenvironment, Provenance, Tectonic setting. DOI: 10.7176/JEES/10-5-03 Publication date: May 31 st 2020
Highlights
The Dahomey Basin is one of the sedimentary basins on the continental margin, it is a pre-cratonic basin that was developed during the initiation of rifting associated with the opening of Gulf of Guinea in early Creataceous to Late Jurassic (Burke et al, 1971; Klemme, 1975; Whiteman, 1982; Kingston et al, 1983)
The basin consists of Cretaceous-Tertiary sequence, which outcrops in an arcuate belt roughly parallel to the ancient coastline and it is characterized by block and transform faulting superimposed across an extensive Paleozoic basin during the breakup of African, North American and South American paleo-continents
This study describes the geochemical composition of Sandstones, Shales and clay of Lewumeji (0 -111m) and Idogun (0 – 54m) well, Eastern Dahomey Basin Southwestern Nigeria (Fig 1)
Summary
The Dahomey Basin is one of the sedimentary basins on the continental margin, it is a pre-cratonic basin that was developed during the initiation of rifting associated with the opening of Gulf of Guinea in early Creataceous to Late Jurassic (Burke et al, 1971; Klemme, 1975; Whiteman, 1982; Kingston et al, 1983). This study describes the geochemical composition of Sandstones, Shales and clay of Lewumeji (0 -111m) and Idogun (0 – 54m) well, Eastern Dahomey Basin Southwestern Nigeria (Fig 1). The geochemical composition of terrigenous sedimentary rocks is a function of the complex interplay of various variables, thereby providing an insight into tectonic settings, provenance, weathering history and transportation history (Bhatia, 1983). Several authors have carried out considerable and intensive researches to characterize and deduce the various lithology, paleoenvironment, provenance, tectonic setting of ancient and recent sediments (Bhatia, 1983; Bhatia and Crook, 1986; Roser and Korsch, 1986, Boboye et al, 2018). The major, trace and rare earth elements are of great importance in provenance and tectonic studies because of their variable signatures during sedimentary processes
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
